1. Field of Invention
The invention relates to a manufacturing method of organic flat light-emitting devices and, in particular, to a manufacturing method of organic flat light-emitting devices that use microstructures in their manufacture.
2. Related Art
In organic flat light-emitting devices, the refraction index of the organic electro-luminescent layer n1 (≈1.7) is very close to that of the transparent anode n2 (≈1.8–2.0), and the refraction index of the transparent substrate n3 (≈1.4–1.5) is smaller than n1 but larger than that of air (≈1). According to Snell's Law, when a beam of light goes through an interface, the product of the refraction index and the sine of the incident angle in the incident medium are equal to that in the refractive medium. When a beam of light goes from the transparent anode into the transparent substrate and the incident angle is greater than sin−1(n3/n2), total reflection occurs and the light is limited to propagation within the organic electro-luminescent layer and the transparent anode. This results in the transparent anode/organic electro-luminescent layer waveguide phenomenon. If the beam of light propagates out from the transparent substrate and the incident angle is greater than sin−1(1/n3), the light will be totally reflected. The light is restricted to propagate within the transparent substrate, resulting in the substrate waveguide phenomenon. However, when the incident angle is smaller than sin−1(1/n3), light will propagate out of the element. One thus sees that only part of the light generated by the organic flat light-emitting device that can propagate out of the element. The rest results in the substrate waveguide phenomenon inside the substrate. From actual measurements, one discovers that the light flux emitted from the organic flat light-emitting device is roughly 20% to 30% of that generated by the organic electro-luminescent layer.
The conventional manufacturing method of organic flat light-emitting devices often uses a substrate with a high refraction index and attaches convex lenses on the light-emitting surface to increase the external quantum efficiency. As shown in FIG. 1, convex lenses 31 with a diameter between 2 mm and 3 mm are attached on the light-emitting surface. If the material of the convex lenses 31 is the same as that of the transparent substrate 32, the light flux of the light-emitting element can be increased by 60% to 100%. If lenses with a higher refraction index are used, the light flux of the element can be increased by 200%. When making the light-emitting element 3, a refraction index matching oil is employed to attach the convex lenses 31 to the light-emitting surface. This is not suitable for long-term use. Another commonly used technique is that disclosed in the U.S. Pat. Nos. 5,936,347 and 6,080,030. The semi-convex lenses or semi-concave lenses are directly formed on a glass substrate by hot-embossing method, thereby increasing the external quantum efficiency of the element. However, the operation temperature for glass hot-embossing method is very high and is likely to make the glass locally deformed. Furthermore, the operation time (for increases and decreases in temperature) is too lengthy for use in mass production.
The elements made using the above-mentioned two manufacturing methods have the drawback of being too thick. It is not suitable for the trend of developing compact light-emitting devices. Moreover, the first conventional method uses a refraction index matching oil to attach the lenses on the light-emitting surface. Elements made in this method are not suitable for long-term use. The other method, however, can easily locally deform the glass substrate. The product yields in the prior art are thus not reliable for commercialization. Furthermore, the manufacturing process requires a longer time. It is therefore highly desirable to create a better method to improve the manufacturing process and product yield.